Thermal type infrared imaging device and fabrication method thereof

ABSTRACT

A fabrication method of a thermal type infrared ray imaging device that includes forming a plurality of diodes in a single crystal silicon layer as first and second thermoelectric conversion parts constituting a thermoelectric conversion part; forming input and output wirings to be connected to a plurality of cells; forming a plurality of opening portions which expose the single crystal silicon substrate; forming a first photothermal conversion layer; and removing selectively a portion of the single crystal silicon substrate via the plurality of opening portions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2002-80066, filed on Mar. 22,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermal type infrared ray imagingdevice and a fabrication method thereof in which a plurality of cellsare provided for each pixel.

2. Related Background Art

Recently, as a thermal type infrared ray image sensor in which a coolingapparatus is unnecessary, a bolometer type made of vanadium oxide usinga micromachine technique and a pyroelectric type made of BST(Barium-Strontium-Titanate) type have been sold commercially. Theseproducts has a heat sensitive part for absorbing infrared ray to raisetemperature, a support leg for thermally separating the heat sensitivepart from a silicon substrate, a horizontal address line for selectingpixels, and a vertical signal line.

This type of infrared ray image sensor absorbs the infrared ray radiatedfrom objects at the heat sensitive part, and detects temperature rise ofthe heat sensitive part by resistance variation and capacitancevariation. Because of this, the support pillar for supporting the heatsensitive part has a structure in which cross section is small andlength is long, in order to enhance adiabatic effect.

However, when the length of the support leg is long, the infrared ray isabsorbed to convert the infrared ray into heat, thereby decreasing areaof the heat sensitive part for converting the heat into an electricsignal. That is, the length of the support leg and the area of the heatsensitive part are trade-off.

When the area of the heat sensitive part decreases, dead area of imagearea increases. When a picture of a faraway small object is taken, aspot focused on an image area becomes about 14 μm of diffraction limit.Because of this, when this spot of 14 μm is focused on non-sensitivearea, no picture can be taken. Accordingly, as shown in FIG. 24,Japanese patent Laid-open publication No. 209418/1998 and so on disclosea structure in which a heat sensitive part 123 is divided into aphotothermal conversion part 125 and a heat sensitive conversion part124, and area of the heat sensitive conversion part 125 is enlarged. InFIG. 24, reference number 121 is a substrate, reference number 122 is abonding pad, reference number 126 is a hollow part, reference number 127is a support leg for supporting the heat sensitive part 123 on thesubstrate 121, reference number 128 is a vertical signal line.

It is possible to estimate emissivity of an object under test, bymeasuring intensity of a plurality of infrared rays radiated from theobjects. Therefore, it is possible to easily identify materials, and toprecisely measure absolute temperature. A method of performing theentire processings by image is disclosed in Japanese Laid-openpublication No. 23261/1997 and Japanese Laid-open publication No.188407/2000. A cooling type image sensor of HgCdTe or GaAlAs/GsAs systemquantum well structure type is used in these documents. The sensor has afeature in which it is possible to easily obtain lamination structure,and an absorption waveband is very narrow. It is possible to selectivelyabsorb the infrared ray of each waveband in each layer of the laminationlayer.

However, in a non-cooling type infrared ray image sensor, for example,Japanese application No. 201400/2001 discloses a method in whichdetection pixels of two wave lengths are alternately disposed for everyline or every column. In the sensor disclosed in this document, anon-sensitive area increases at each waveband, and it becomes difficultto take a picture of a faraway small object.

Conventionally, it is possible to estimate emissivity of the objectunder test by measuring a plurality of infrared rays emitted fromobjects. Therefore, it is possible to identify a material of the objectunder test, and to precisely measure the absolute temperature. However,there was a problem in which the non-sensitive area at each wavebandincreases, and it became difficult to take a picture of the farawaysmall object.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a thermal type infraredray imaging device and a fabrication method thereof capable of obtainingexcellent imaging properties by preventing increase of the non-sensitivearea at each waveband.

In order to achieve the foregoing object, a thermal type infrared rayimaging device, comprising:

a plurality of cells arranged on a substrate each having a photothermalconversion part which converts an infrared ray into heat, and athermoelectric conversion part which is provided below said photothermalconversion part and which converts the heat generated by saidphotothermal conversion part into an electric signal;

a selection part which selects some cells among said plurality of cells;and

an output part which outputs the electric signal generated by saidthermoelectric conversion part of each of the selected cells,

wherein said photothermal conversion part includes:

a first photothermal conversion layer; and

a second photothermal conversion layer provided over and apart from saidfirst photothermal conversion layer, which converts an infrared raywithin a waveband different from a waveband of said first photothermalconversion layer into heat,

wherein said thermoelectric conversion part includes:

a first thermoelectric conversion part which converts the heat generatedby said first photothermal conversion layer into the electric signal;and

a second thermoelectric conversion part which is thermally separatedfrom said first thermoelectric conversion part, and which converts theheat generated by said second photothermal conversion layer into theelectric signal.

Furthermore, a thermal type infrared ray imaging device, comprising:

a plurality of cells arranged on a substrate each having a photothermalconversion part which converts an incident infrared ray into heat, and athermoelectric conversion part which is provided below said photothermalconversion part and which converts the heat generated by saidphotothermal conversion part into an electric signal;

a selection part which selects some cells among said plurality of cells;and

an output part which outputs the electric signal generated by saidthermoelectric conversion part of each of the selected cells;

wherein said photothermal conversion part has a plurality ofphotothermal conversion layers which convert infrared rays withindifferent wavebands into heat, said photo thermal conversion layersbeing disposed apart from each other in a vertical direction; and

said thermoelectric conversion part has a plurality of thermoelectricconversion parts which convert the heat generated by said plurality ofphotothermal conversion layers into the electric signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section view showing a structure for one pixel of thethermal type infrared ray element of one embodiment according to thepresent invention.

FIG. 2 is a top face view of the thermal type infrared ray imagingdevice of the present embodiment.

FIGS. 3A and 3B are top face views extracting a thermoelectricconversion part and a photothermal conversion layer which aresubstantial parts of FIG. 2.

FIG. 4 is a top surface view showing a layout of a thermal type infraredray imaging device of the present embodiment.

FIG. 5 is a conceptual view for explaining operation of the thermal typeinfrared ray imaging device of the present embodiment.

FIG. 6 is a cross section view showing fabrication step of the thermaltype infrared ray imaging device of the first embodiment of the presentinvention.

FIG. 7 is a cross section view following to FIG. 6.

FIG. 8 is a cross section view following to FIG. 7.

FIG. 9 is a cross section view following to FIG. 8.

FIG. 10 is a cross section view following to FIG. 9.

FIG. 11 is a cross section view following to FIG. 10.

FIG. 12 is a cross section view following to FIG. 11.

FIG. 13 is a cross section view following to FIG. 12.

FIG. 14 is a cross section view following to FIG. 13.

FIG. 15 is a cross section view following to FIG. 14.

FIG. 16 is a cross section view following to FIG. 15.

FIG. 17 is a cross section view following to FIG. 16.

FIG. 18 is a cross section view following to FIG. 17.

FIG. 19 is a cross section view following to FIG. 18.

FIG. 20 is a cross section view following to FIG. 19.

FIG. 21 is a cross section view following to FIG. 20.

FIG. 22 is a cross section view following to FIG. 21.

FIG. 23 is a cross section view following to FIG. 22.

FIG. 24 is a cross section view showing configuration of one pixel of aconventional thermal type infrared ray imaging device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, one embodiment of a thermal type infrared ray imagingdevice according to the present invention will be described withreference to drawings.

The thermal type infrared ray imaging device of one embodiment describedhereinafter detects infrared ray of multiple wavelengths, and has astructure in which a plurality of pixels for detecting infrared rays arearranged in matrix shape.

FIG. 1 is a cross section view showing a structure for one pixel of thethermal type infrared ray element of one embodiment according to thepresent invention. FIG. 2 is a top surface view of the thermal typeinfrared ray imaging device of the present embodiment, and FIGS. 3A and3B are top surface views extracting a thermoelectric conversion part andan photothermal conversion layer which are substantial parts of FIG. 2.

As shown in FIG. 1, a thermoelectric conversion part 17 (a secondthermoelectric conversion part and a thermoelectric conversion part forsecond waveband) of the infrared ray detection pixels and athermoelectric conversion part 18 (a first thermoelectric conversionpart and a thermoelectric conversion part for first waveband) of theinfrared detection pixels are provided at the state of floating on ahollow area 20 formed inside the single crystal silicon substrate 11 a,and are supported on the single crystal silicon substrate 11 a by asupport leg 12. Here, the hollow area 20 is formed by selectivelyremoving by etching, for example, a portion of the single crystalsilicon substrate 11 a of the SOI (Silicon On Insulator) substratecontaining the single crystal silicon substrate 11 a, the embedded oxidefilm 11 b band the single crystal silicon layer 11 c. Reference number19 a is a groove portion formed between the support leg 12 and thesingle crystal silicon substrate 11 a, and reference number 19 b is agroove portion formed between the thermoelectric conversion parts 17 and18. It is possible to effectively perform temperature variation of thethermoelectric conversion part by the incident infrared ray, byproviding the thermoelectric conversion parts 17 and 18 and the supportleg 12 on the hollow structure 20. Although reference number 11 b is theburied oxide film on the SOI substrate as mentioned above, this film isalso provided below under surface of the thermoelectric converters 17and 18.

In FIG. 1, the thermoelectric conversion parts 17 and 18 look to beformed by being physically segmentalized. However, as shown in topsurface view of FIG. 2, the thermoelectric conversion parts 17 and 18are in reality formed on an all-in-one device region 10. That is, thedevice region 10 is supported on the single crystal silicon substrate 11a by the support leg 12, and grooves 19 b with two stripes are formed onportions of the device region 10 in parallel to each other. Thethermoelectric conversion part 17 is provided between the grooves 19 bwith two stripes, and the thermoelectric conversion part 18 is providedat outer area of the grooves 19 b. Reference number 11 d is a deviceisolation insulation film provided between the thermoelectric conversionparts 17 and 18, and the device isolation insulation film 11 d is madeof, for example, silicon dioxide.

As shown in FIG. 3A, the thermoelectric conversion part 17 hasthermoelectric conversion elements 17 a, 17 b, 17 c and 17 d. Thethermoelectric conversion elements 17 a, 17 b, 17 c and 17 d areconnected in series by using connection wirings.

The thermoelectric conversion elements 17 a, 17 b, 17 c and 17 d areconsisted of diodes such as pn junction, respectively. The diodes aremade of the single crystal silicon layer of the SOI substrate. A p layerand an n layer located at both ends of pn junction of the diode may bearranged in a direction parallel to the substrate surface, or may belaminated in a direction vertical to the substrate surface.

As shown in FIG. 3B, the thermoelectric conversion part 18 has thethermoelectric conversion elements 18 a, 18 b, 18 c and 18 d, and thethermoelectric conversion elements 18 a and 18 b are disposed at oneside of two grooves 19 b, and the thermoelectric conversion elements 18c and 18 d are disposed at the other side of two grooves 19 b.

These thermoelectric conversion elements 18 a, 18 b, 18 c and 18 d areconnected in series, similarly to the thermoelectric conversion part 17.For example, these thermoelectric conversion elements 18 a, 18 b, 18 cand 18 d are consisted of diodes having pn junction formed in thesilicon layer.

As shown in FIG. 3A, the photothermal conversion layer 14 a is supportedby the support pillar 14 b on the thermoelectric conversion elements 17a, 17 b, 17 c and 17 d of the thermoelectric conversion part 17 (asecond thermoelectric conversion part and a thermoelectric part forsecond waveband), and is provided spreading in a horizontal direction ofthe substrate. As shown in FIG. 3B, four photothermal conversion layers13 a are supported by the support pillar 13 b on the thermal electricconversion elements 18 a, 18 b, 18 c and 18 d, and are provided in thehorizontal direction of the substrate.

As shown in FIG. 1, the photothermal conversion layer 13 a is disposedbelow the photothermal conversion layer 14 a. As the photothermalconversion layer 13 a, for example, BPSG (Bolon Phosphorus doped inSilicate Glass) or BSG (Bolon doped in Silicate Glass), PSG (Phosphorusdoped in Silicate Glass) and so on are used. As the photothermalconversion layer 14 a, for example, a lamination film formed bylaminating silicon nitride film on silicon dioxide), FSG (Fluorosisdoped in Silicate Glass) and so on are used.

Hereinafter, the support leg 12 will be explained in detail. The supportleg 12 has wirings 12 a, 12 b and 12 c are formed inside a support beamformed of an insulation film such as silicon dioxide or silicon nitride.The support leg 12 is disposed to surround the device region 10 betweenthe single crystal silicon substrate 11 a and the device region 10 inwhich the thermoelectric electric conversion parts 17 and 18 are formedin order to support the device region.

Heat conductance of the support leg 12 is not more than about 2×10⁻⁷W/K, and the support leg 12 thermally separates the device region 10from the single crystal silicon substrate 11 a. The number of thesupport legs 12 may not be two pieces. The number of the support legsmay be more than two or less than two, if necessary. The wirings 12 aand 12 b are output wirings for a first waveband and a second waveband,as described below in detail. The wiring 12 c is a common input wiringfor first waveband and the second waveband.

The thermoelectric conversion part 18 has the thermoelectric conversionelements 18 a, 18 b, 18 c and 18 d connected in series in order. One endof the output wiring 12 a is connected to the thermoelectric conversionelement 18 d disposed at the most outer side. The connection point ofone end of the output wiring 12 a is omitted in FIG. 2. The other end ofthe output wiring 12 a is connected to a vertical signal wiring 15 for afirst waveband.

The thermoelectric conversion part 17 has thermoelectric conversionelements 17 a, 17 b, 17 c and 17 d connected in series in order. One endof the output wiring 12 b is connected to the thermoelectric conversionelement 17 d disposed at the most outer side. The other end of theoutput wiring 12 b is connected to a vertical signal wiring for secondwaveband 16.

As shown in FIG. 2, the vertical signal wiring for first waveband 15 andthe vertical signal wiring for second waveband 16 are provided inparallel to each other, and these wirings 15 and 16 are commonlyconnected to a plurality of pixels disposed in column direction. On theother hand, one end of the input wiring 12 c is connected to thethermoelectric conversion element 18 a of the thermoelectric conversionpart 18 disposed at the nearest location to input side (horizontalsignal line side) and the thermoelectric conversion element 17 a of thethermoelectric conversion part 17 disposed at the nearest location toinput side (horizontal signal line side). The other end of the inputwiring 12 c is connected to a common horizontal signal line wiring(horizontal address line) 21 for the first and second wavebands. Thehorizontal signal wiring (horizontal address line) 21 is commonlyconnected to pixels disposed in row directions.

FIG. 4 is a top surface view showing a layout of a thermal type infraredray imaging device of the present embodiment. In FIG. 4, referencenumber 51 is an image area within which detection pixels of theabove-mentioned infrared ray imaging devices are disposed in matrixshape. Reference number 52 is a vertical shift register circuit to whichthe horizontal address line 21 is connected. Reference number 53 is ahorizontal shift register circuit to which the vertical signal wiringfor first waveband 15 and the vertical signal wiring for second waveband16 are connected, reference number 55 is a signal processing circuit forfirst waveband, reference number 56 is a signal processing circuit forsecond waveband, reference number 57 is a signal output circuit forfirst waveband, reference number 58 is a signal output circuit forsecond waveband, reference number 59 is a signal output pad for firstwaveband, reference number 60 is a signal output pad for secondwaveband, reference number 54 is a bonding pad for supplying drivepulses of the other shift register or an amplification circuit.

Next, operation of the thermal type infrared ray imaging device of thepresent embodiment will be explained. FIG. 5 is a conceptual view forexplaining operation of the thermal type infrared ray imaging device ofthe present embodiment. As shown in FIG. 5, reference number 32 is aninfrared ray incident from outside. The infrared ray is concentrated bya lens 31 and incident to the image area 51 of the above-mentionedthermal type infrared ray imaging device.

The infrared ray of second waveband (for example, waveband 8–12 μm)among the incident infrared ray is absorbed in the photothermalconversion layer 14 a in order to perform heat conversion. The generatedheat is transmitted to the thermoelectric conversion part 17 via thesupport pillar 14 b, and is converted into the electric signal by thethermoelectric conversion part 17. The electric signal generated by thisconversion is transmitted to the vertical signal wiring for secondwaveband 16 via the output wiring 12 b. And then via the horizontalshift register circuit 53 of FIG. 4, the electric signal is subjected tosignal processings by the signal processing circuit 56 for secondwaveband, and then is outputted from the signal output pad for secondwaveband 60.

The infrared ray of first waveband (for example, waveband is 3–5 μm) notabsorbed by the photothermal conversion layer 14 a is absorbed by thephotothermal conversion layer 13 a in order to perform heat conversion.The generated heat is transmitted to the thermoelectric conversion part18 via the support pillar 13 b in order to perform conversion toelectric signal. The electric signal generated by this conversion istransmitted to the vertical signal wiring for first waveband 15 via theoutput wiring 12 a, and is subjected to signal processings by the signalprocessing circuit for first waveband 55 via the horizontal shiftregister circuit 53 of FIG. 4. And then the electric signal is outputtedfrom the signal output pad for first waveband 59 via the signal outputcircuit for first waveband 57.

Thus, according to the present embodiment, it is possible to separatelydetect and output the infrared ray of the first waveband and theinfrared ray of the second waveband. Because of this, it is possible toestimate emissivity of the object under test by obtaining intensity of aplurality of infrared rays radiated from the object. Accordingly, it ispossible to easily identify materials of the object and to preciselymeasure absolute temperature, thereby improving contrast of image of theinfrared ray and colorizing the image.

Especially, according to the present embodiment, when the infrared rayof first waveband and the infrared ray of second waveband are separatelydetected, the photothermal conversion layer corresponding to theinfrared rays of a plurality of wavebands as shown in above-mentionedembodiment is doubly disposed in the direction vertical to the substratesurface, and further a plurality of thermoelectric conversion parts forconverting the heat generated by the photothermal conversion layers intoheat are disposed to be integrated to one pixel. Because of this, it ispossible to prevent increase of non-sensitive area for the infrared rayswithin wavebands, and to sensitively take a picture of a faraway smallobject.

Furthermore, the grooves 19 b of two stripes are provided between thethermoelectric electric conversion parts 17 and 18. Therefore, thermalisolation between both of the thermoelectric conversion parts 17 and 18is ensured. It is possible to improve accuracy of heat sensitivity inthe thermoelectric conversion part, thereby obtaining more excellentinfrared ray image.

As compared with the case where pixels having different sensitivewavelengths are alternatively arranged for every column known as theconventional technique, even if the imaging size and the number ofpixels are the same, the image area becomes small. Therefore, it ispossible to downsize optical mechanism and to realize multi-wavelengthinfrared ray image sensor at low price. Furthermore, when the image areasize is the same, it is possible to enlarge the imaging size, and torealize high-sensitive and multi-wavelength infrared ray image sensor.

In the above-mentioned embodiment, the photothermal conversion layer 14a of the upper layer converts into heat the infrared ray within wavebandlonger than that of the photothermal conversion layer 13 a of the lowerlayer. Thus, because the photothermal conversion layer 14 a capable ofabsorbing the infrared ray within longer waveband to the upper layerportion through which the infrared ray passes on ahead is disposed, itis possible to effectively absorb the infrared ray within a longwaveband which is more reflective in the upper layer, and to restrictdeterioration of absorption efficiency such as reflection. Furthermore,the photothermal conversion layer 13 a for absorbing the infrared raywithin short waveband is provided to the lower layer portion. It ispossible to effectively absorb in total the infrared rays withinmultiple-waveband.

Furthermore, as a structure of the photothermal conversion layer, in thecase where the photothermal conversion layer 14 a with large area isprovided to the upper layer, and the photothermal conversion layer 13 awith small area is provided to the lower layer, fabrication process iseasier than in the case where disposition of the upper layer and thelower layer is opposite. Even in this point, the structure of thepresent embodiment is desirable.

Moreover, the photothermal conversion layer 14 a of large area tends toabsorb the infrared ray of longer wavelength, and the photothermalconversion layer 13 a of small area tends to absorb the infrared ray ofshorter wavelength. Because of this, it is possible to improveabsorption efficiency of the infrared ray by enlarging the area of thephotothermal conversion layer 14 a of the upper layer more than that ofthe photothermal conversion layer 13 a of the lower layer. Thus, thepresent embodiment excels in absorption efficiency of the infrared rayand fabrication process.

Especially, it is desirable that the size of acceptance surface of thephotothermal conversion layer 14 a of the upper layer is not less thanat least 10 μm per side, and the size of the acceptance surface of thephotothermal conversion layer 13 a of the lower layer is not less thanat least 3 μm and is less than 8 μm.

Next, fabrication method of the thermal type infrared ray imaging deviceof FIG. 1 will be explained. FIGS. 6–23 are cross section views offabrication steps for explaining fabrication methods of the thermal typeinfrared ray imaging device of FIG. 1. Each view shows a cross sectionview cut off by A–A′.

First of all, as shown in FIG. 6, an SOI substrate which is formed bylaminating an buried silicon dioxide film 11 b and a single crystalsilicon layer 1 c on a single crystal silicon support substrate 11 a isprepared as a semiconductor substrate.

Next, an STI (Shallow-Trench-Isolation) fabrication is performed,similarly to device isolation in general LSI fabrication steps. Morespecifically, as shown in FIG. 7, the device isolation area isprescribed by using photolithography. The single crystal silicon layer11 c of the device isolation area is removed by etching by using atechnique such as RIE (Reactive-Ion-Etching). After then, the deviceisolation silicon dioxide film 11 d is embedded by using a techniquesuch as CVD (Chemical-Vapor-Deposition), and then is evened by using atechnique such as CMP (Chemical-Mechanical-Polishing). At this time, thearea of the support pillar is also defined as the device isolation area,and the device isolation silicon dioxide film lid is embedded.

Next, a diode having pn junction is formed of the single crystal siliconlayer 11 c. After forming the diode, the device isolation silicondioxide film 11 d may be formed.

It is possible to use a technique such as injection of impurity ion,heat treatment activation and diffusion in order to form the diode. Forexample, when n⁺ type silicon layer is formed on surface of p typesilicon layer, impurity ion As may be injected by, for example,acceleration voltage 50 kv and the dose amount 5×10¹⁵ cm⁻².

FIGS. 7–23 show an example in which n type (p type) conduction typesemiconductor layer 48 b is selectively formed on a surface of a p type(n type) conduction type semiconductor layer 48 a, as a diode.

The diode consisted of the p type conduction type semiconductor layer 48a and the n type conduction type semiconductor layer 48 b of FIGS. 7–23corresponds to diodes 17 a, 17 b, 17 c and 17 d of FIG. 3A constitutingthe thermoelectric conversion part 17 and diodes 18 a, 18 b, 18 c and 18d of FIG. 3B constituting the thermoelectric conversion part 18.

Next, as shown in FIG. 8, after a metal layer such as aluminum is formedon the substrate, the metal layer is patterned by RIE and so on in orderto form an input wiring 12 c and an output wiring 12 a. The outputwiring 12 a is an output wiring for first waveband as explained in thefirst embodiment, and is connected to the diode shown in FIG. 3B atcross section location different from the cross section of FIG. 8. Theinput wiring 12 c is a common input wiring for first and secondwavebands, and connected to the diode 18 a shown in FIG. 3B and thediode 17 a shown in FIG. 3A at cross section location different from thecross section of FIG. 8.

Next, as shown in FIG. 9, after an interlayer insulation film 11 e suchas silicon dioxide is formed on the substrate, an output wiring 12 b isformed by using the metal film. The output wiring 12 b is connected tothe diode 17 d at cross section location different from the crosssection of FIG. 9 via a contact hole not shown.

Next, as shown in FIG. 10, an interlayer insulation film 11 f such assilicon dioxide is formed on the substrate including a top surface ofthe output wiring 12 b.

Next, as shown in FIG. 11, connection wirings 15′ and 16′, the verticalsignal wiring for first waveband 15 and the vertical signal wiring forsecond waveband 16 are formed on the upper surface of the interlayerinsulation film 11 f. The connection wiring 15′ is a wiring for directlyconnecting diodes 18 a, 18 b, 18 c and 18 d. The connection wiring 16′is a wiring for directly connecting diodes 17 a, 17 b, 17 c and 17 d.The connection wirings 15′ and 16′ are connected to the diodes viacontact holes not shown.

Next, as shown in FIG. 12, an interlayer insulation film 11 g such assilicon dioxide is formed on the substrate so as to cover the connectionwirings 15′ and 16′, the vertical signal wiring for first waveband 15and the vertical signal wiring for second waveband 16. Subsequently, asshown in FIG. 13, an interlayer insulation film 11 h such as silicondioxide is formed on the substrate.

Next, as shown in FIG. 14, an etching hole 71 is formed from theinterlayer insulation film 11 h through the buried silicon dioxide film11 b by RIE by using etching mask not shown. The etching hole 71 isformed at surrounding area of the input wiring 12 c and is also formedin the area between the thermoelectric conversion parts 17 and 18.

After then, as shown in FIG. 15, a sacrifice layer 72 is formed on thesubstrate by using CVD method. Material of the sacrifice layer 72 isamorphous silicon or polyimide. At this time, the sacrifice layer 72 isembedded in the etching hole 71 shown in FIG. 14.

Next, as shown in FIG. 16, a mask not shown is provided on the sacrificelayer 72. A portion of the sacrifice layer 72 is removed by etching byperforming RIE using the mask. As a result, the sacrifice pattern 72′ isremained in a peripheral area of pixels (including areas on the outputwirings 12 a and 12 b and the input wiring 12 c, and within thesurrounding etching hole 71), and is remained in the etching hole 71between the thermoelectric conversion part 17 and the thermoelectricconversion part 18.

Next, as shown in FIG. 17, for example, BPSG (Bolon-Phosphorus dopedSilicate Glass) film 73 is formed on the substrate. Subsequently, asshown in FIG. 18, the BPSG film 73 is etched by using the mask. The BPSGpattern 73′ obtained as this result corresponds to the photothermalconversion layer 13 a and the support pillar 13 b of FIG. 1. In thepresent embodiment, the size of the BPSG pattern 73′ is 5 μm per sideand the thickness thereof is about 0.4 μm.

Next, as shown in FIG. 19, the sacrifice layer 74 is formed on thesubstrate by CVD method. Material of the sacrifice layer 74 is amorphoussilicon or polyimide. Furthermore, as shown in FIG. 20, a mask not shownis provided on the sacrifice layer 74. A portion of the sacrifice layer74 is removed by etching by performing RIE using the mask. As a result,the sacrifice layer pattern 74′ remains in an area covering the BPSGpattern 73′ (including an areas on the output wiring 12 a and the inputwiring 12 c, and an area on the etching hole between the thermoelectricconversion parts 17 and 18).

Next, as shown in FIG. 21, the laminate film 75 obtained by laminatingthe silicon dioxide film and the silicon nitride film is formed on thesubstrate. Furthermore, the laminate film 75 is etched by using the masknot shown. Therefore, the laminate film pattern 75 is formed as thephotothermal conversion layer 14 a and the support pillar 14 b ofFIG. 1. According to the present embodiment, the size of the laminatefilm pattern is 10 μm per side, and the thickness of the silicon dioxidefilm is about 0.4 μm, and the thickness of the silicon nitride film isabout 0.2 μm. The laminate film pattern 75 is selectively removed byetching so as to be able to remove the material of the sacrifice layerby etching.

Next, as shown in FIG. 22, in order to selectively remove the sacrificelayer pattern 72′, 74′ and the material of the sacrifice layer embeddedin the etching hole 71, the material of the sacrifice layer is etched byusing alkalis etching liquid solution such as KOH or TMAH(Tetra-Methyl-Ammonium-Hydroxide). In this step, the interlayerinsulation films 11 e–11 h, the embedded silicon dioxide film 11 b, theBPSG patter 73′ and the laminate film pattern 75 are not etched. As aresult, the single crystal silicon support substrate 11 a of the bottomsurface of the etching hole formed in FIG. 18 is exposed in order toform a void portion 19 a and the grooves 19 b, a void between the BPSGpattern 73′ corresponding to the photothermal conversion layer 13 a andthe support pillar 13 b, and the laminate film 75 corresponding to thephotothermal conversion layer 14 a and the support pillar 14 b isformed, and a void is formed below the BPSG pattern 73′ corresponding tothe photothermal conversion layer 13 a.

After then, as shown in FIG. 23, the etching liquid such as TMAH issupplied to the single crystal silicon support substrate 11 a via theetching hole 71, and the single crystal silicon support substrate 11 ais subjected to anisotropic etching. A hollow portion is generated onthe single crystal support substrate 11 a under the pixels of thethermal type infrared ray imaging device in order to form the hollowstructure 20.

By the above-mentioned steps, it is possible to form the thermal typeinfrared ray imaging device of the first embodiment for one pixel shownin FIG. 1. In the present embodiment, the thermal type infrared rayimaging device has 320×240 pixels, each pixel arranging in two dimensionarray shape, and being formed on the same procedure as theabove-mentioned procedure.

Although the image area 51 of FIG. 5 can be formed by theabove-mentioned steps, area except for the image area 51 can be formedby the ordinary semiconductor process. In a sequence of etching steps ofFIGS. 22 and 23, a protection layer is provided in order to preventetching for these areas so that the area except for the image area 51 isnot etched. As the protection layer, it is possible to use a silicondioxide film formed by CVD as the protection layer.

Thus, according to the present embodiment, the infrared ray of firstwaveband and the infrared ray of second waveband are separatelydetected. Because the infrared rays can be separately outputted, it ispossible to precisely measure the intensity of a plurality of infraredrays radiate from the objects and to estimate emissivity of the objectunder test. Therefore, it is possible to easily identify the material ofthe object and to precisely measure the absolute temperature.Accordingly, it is possible to improve contrast of image by the infraredray and to realize colorization of image.

Especially, according to the present embodiment, in order to separatelydetect the infrared rays of first and second wavebands, the photothermalconversion layers corresponding to the infrared rays of a plurality ofwavebands are doubly disposed in the direction vertical to the substratesurface, and a plurality of thermoelectric conversion parts forconverting heat generated by the photothermal conversion layers intoelectric signal are disposed by integrating in one pixel. Therefore, itis possible to prevent increase of the non-sensitive areas for theinfrared rays of the respective wavebands, and to sensitively take apicture of a faraway small object.

Furthermore, it is possible to improve heat sensitive accuracy in thethermoelectric part by ensuring heat isolation between both thethermoelectric conversion parts, thereby obtaining more excellentinfrared ray image.

The present invention is not limited to the above-mentioned embodiment.For example, as a thermal separation structure, a structure providingthe groove between a plurality of thermal electric conversion parts hasbeen adopted. However, despite of such a structure, after a V shapegroove is formed, it is possible to use the other structure such as thestructure in which porous ceramics and so on is embedded in the V shapegroove.

It is possible to use an element except for a diode as a thermoelectricconversion part. For example, it is possible to use the other devicessuch as an enhanced type MOS transistor, a depletion type MOStransistor, a combination of these MOS transistors, a bolometer ofvanadium oxide or amorphous silicon, and so on.

Furthermore, according to the present embodiment, the hollow structurehas been formed between the support substrate and the pixel of thethermal type infrared ray imaging device, by etching the single crystalsilicon support substrate of the SOI substrate. However, besides themethod and the structure using the SOI substrate, it may be possible toadopt a method and a structure of forming the insulation film such asoxide or nitride formed on the support substrate, and poly-crystal ormono-crystal silicon layer in order from bottom, and the surface of thesupport substrate and the insulation film are removed by etching inorder to form the hollow structure.

Furthermore, although aluminum has been used as a wiring material in theabove-mentioned embodiment, it is possible to use the other metalmaterial. Especially, the output wirings 12 a and 12 b, the input wiring12 c, the vertical signal wiring for first waveband 15 and the verticalsignal wiring for second waveband 16 are formed of polycide structure atthe same fabrication step as that of forming the gate electrode of theMOS transistor of the peripheral circuit, thereby simplifyingfabrication process. The present invention is applicable to a poly-metalstructure (laminate structure of a polysilicon layer and a metal layer).The poly-metal structure can be formed at the same fabrication step asthat of the gate electrode of the MOS transistor of the peripheralcircuit. If the poly-metal structure is adopted, it is possible toreduce thermal noise due to electric resistance of the wiring portion ofthe support leg (the output wirings 12 a and 12 b and the input wiring12 c), thereby improving sensitivity. In this case, as a laminatestructure of the support leg wirings (the output wirings 12 a and 12 band the input wiring 12 c), for example, it is possible to form thelaminate film made of a titan nitride film as a barrier metal and atungsten film for low resistance on the polysilicon layer.

Furthermore, it is possible to selectively leave the silicon nitridefilm on a side wall of the support leg wiring. In this case, it ispossible to form the support leg wiring by using the same layer as thesilicon nitride film formed on the gate sidewall of the MOS transistorsof the peripheral circuit. Because of this, it is possible todrastically shorten the number of steps. Especially, it is possible tofabricate the high sensitive support structure at high yield and lowcost, while getting the most out of compliance of process, by using thestep of forming silicon nitride film and the step of forming the supportleg wirings at the same layer as the gate electrode of the MOStransistor of the peripheral circuit.

Besides, it is possible to modify the present invention at range whichdoes not deviate from purposes of the present invention, if necessary.

1. A fabrication method of a thermal type infrared ray imaging devicecomprising a plurality of cells arranged on an SOI (Silicon OnInsulator) substrate consisted of a single crystal silicon substrate, anembedded oxide film and a single crystal silicon layer, each of saidplurality of cells having a photothermal conversion part which convertsan infrared ray into heat, and cell thermoelectric conversion part whichis provided below said photothermal conversion part and which convertsthe heat generated by said photothermal conversion part into an electricsignal; a selection part which selects some cells among said pluralityof cells; and an output part which outputs the electric signal generatedby said cell thermoelectric conversion part of each of the selectedcells, wherein said photothermal conversion part includes: a firstphotothermal conversion layer; and a second photothermal conversionlayer provided over and apart from said first photothermal conversionlayer, which converts an infrared ray within a waveband different from awaveband of said first photothermal conversion layer into heat, whereinsaid cell thermoelectric conversion part includes: a firstthermoelectric conversion part which converts the heat generated by saidfirst photothermal conversion layer into the electric signal; and asecond thermoelectric conversion part which is thermally separated fromsaid first thermoelectric conversion part, and which converts the heatgenerated by said second photothermal conversion layer into the electricsignal, the fabrication method comprising: forming a plurality of diodesin said single crystal silicon layer as said first and secondthermoelectric conversion parts constituting said cell thermoelectricconversion part separated from each other; forming input and outputwirings to be connected to said plurality of cells; covering a topsurface of said SOI substrate including said input and output wiringswith a first insulation film, and then forming a plurality of openingportions which expose said single crystal silicon substrate; forming afirst sacrifice layer inside said plurality of opening portions and thetop surface of said first insulation film; removing selectively saidfirst sacrifice layer by etching; forming a second insulation film as amaterial of said first photothermal conversion layer constituting aportion of said photothermal conversion part on said first sacrificelayer remained by etching and said first insulation layer exposed byremoving said first sacrifice layer by etching; forming said firstphotothermal conversion layer by removing a portion of said secondinsulation layer by etching; forming a second sacrifice layer on saidfirst photothermal conversion layer and said first insulation layerexposed by removing said second insulation film by etching; removingselectively said second sacrifice layer; forming a third insulation filmas a material of said second photothermal conversion film constituting aportion of said photothermal conversion part on said second sacrificelayer remained by etching and said first insulation layer exposed byremoving said second sacrifice layer by etching; removing selectivelysaid third insulation film by etching; removing selectively materials ofsaid first and second sacrifice layers by etching; and removingselectively a portion of said single crystal silicon substrate via saidplurality of opening portions.
 2. The fabrication method of the thermaltype infrared ray imaging device according to claim 1, wherein saidfirst and second photothermal conversion layers convert the infraredrays within different wavebands into heat.
 3. The fabrication method ofthe thermal type infrared ray imaging device according to claim 1,wherein said second photothermal conversion layer is made of a silicondioxide, and said first photothermal layer is made of a silicate glasscontaining boron and phosphorus.